Kinetics of Cr(VI) removal by Mg–Al layered double hydroxide doped with Fe2+

The removal of Cr(VI) from aqueous solution by a Mg–Al layered double hydroxide (Mg–Al LDH) doped with Fe 2+ increased with time and temperature. Cr(VI) removal could not be described by first-order reaction kinetics, but it was well represented as a pseudo second-order reaction. The apparent rate constants at 10, 30, and 60 °C were 0.9 × 10 −3 , 1.2 × 10 −3 , and 2.2 × 10 −3 g mmol −1 min −1 , respectively, and the apparent activation energy was 14.5 kJ mol −1 . This value confirms that the rate-determining step for Cr(VI) removal is chemical adsorption involving the anion exchange of Cr 2 O 7 2− with intercalated Cl − and the adsorption of Cr 2 O 7 2− on the surface of the produced FeO(OH).